Laser-Doppler measurement of the velocity and diameter of bubbles using the triple-peak technique

Abstract The velocity and diameter of nitrogen bubbles rising in quiescent water were simultaneously measured by a dual-beam laser-Doppler anemometer. The range of bubble diameters was 0.8–1.8 mm. The triple-peak technique was used to obtain the bubble diameter from the anemometer signal. Using a single stream of bubbles, the horizontal area of the bubble-detection region was proportional to the square of the bubble diameter. Using additional streams of bubbles to generate an optical disturbance, the probability of detecting a valid signal decreased linearly with increasing bubble flowrate of the additional streams and was independent of their location and number. The maximum void fraction was 0.01.